U.S. patent number 6,980,823 [Application Number 10/206,630] was granted by the patent office on 2005-12-27 for intermediate wake mode to track sleep clock frequency in a wireless communication device.
This patent grant is currently assigned to Qualcomm Inc.. Invention is credited to Baaziz Achour, Raghu Challa, Robbin D. Hughes.
United States Patent |
6,980,823 |
Challa , et al. |
December 27, 2005 |
Intermediate wake mode to track sleep clock frequency in a wireless
communication device
Abstract
Various techniques for improving a wireless communication device
are described. The techniques may include reducing power in a
wireless communication device for a first sleep period and then
increasing power in the wireless communication device for an
intermediate wake period after the first sleep period to estimate
an error of the sleep clock. The method may further include
reducing power in the wireless communication device for a second
sleep period after the intermediate wake period. The intermediate
wake mode implemented during the intermediate period can be used to
estimate the error of the sleep clock without performing one or
more tasks associated with an awake mode, such as demodulation. The
techniques may facilitate the effective use of low frequency low
power clocks for sleep mode, even when relatively large slot cycles
are defined within a slotted paging system.
Inventors: |
Challa; Raghu (San Diego,
CA), Achour; Baaziz (San Diego, CA), Hughes; Robbin
D. (San Diego, CA) |
Assignee: |
Qualcomm Inc. (San Diego,
CA)
|
Family
ID: |
27616327 |
Appl.
No.: |
10/206,630 |
Filed: |
July 26, 2002 |
Current U.S.
Class: |
455/522;
375/E1.014; 455/21; 455/574 |
Current CPC
Class: |
H04W
56/0035 (20130101); H04B 1/70756 (20130101); H04W
52/029 (20130101); Y02D 30/70 (20200801); H04B
2201/70709 (20130101); H04W 52/0216 (20130101) |
Current International
Class: |
H04B 007/00 () |
Field of
Search: |
;455/522,343,574,550,572,506,69,502,67.6,517,38.3,21 ;370/311 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Lin et al., "Modeling the Sleep Mode For Cellular Digital Packet
Data", IEEE Communications Letters, vol. 3, No. 3, pp. 63-65, Mar.
1999. .
Nagata et al., "Control Techniques and Power Saving Effects of
Intermittent Operation in Radio Units", Vehicular Technology
Conference, Tampa, Jun. 1-3, 1987, pp. 560-566..
|
Primary Examiner: Gesesse; Tilahun
Assistant Examiner: Trinh; Tan
Attorney, Agent or Firm: Wadsworth; Philip R. Brown; Charles
D. Pappas; George C.
Parent Case Text
RELATED APPLICATIONS
This application claims the benefit of provisional U.S. Application
Ser. No. 60/353,475, entitled "INTERMEDIATE WAKE MODE TO TRACK
SLEEP CLOCK FREQUENCY IN A WIRELESS COMMUNICATION DEVICE," filed
Jan. 31, 2002, which is incorporated herein by reference in its
entirety for all purposes.
Claims
What is claimed is:
1. A method comprising: reducing power in a wireless communication
device to place the wireless communication device in a sleep mode
for a first sleep period; increasing power in the wireless
communication device to place the wireless communication device in
an intermediate wake made for an intermediate wake period after the
first sleep period, the intermediate wake mode being a mode in
which the wireless communication device is not fully powered and
not demodulating a paging channel but is estimating an error of a
sleep clock; and reducing power in the wireless communication
device for a second sleep period to place the wireless
communication device in the sleep mode immediately after the
intermediate wake period so that the paging channel is not
demodulated by the wireless communication device between the first
sleep period and the second sleep period.
2. The method of claim 1, further comprising increasing power in
the wireless communication device for an awake period after the
second sleep period.
3. The method of claim 2, further comprising during the awake
period: estimating the error of the sleep clock based on a time
that a pilot signal is received; correcting for the error in the
sleep clock; and demodulating a paging signal.
4. The method of claim 1, wherein the intermediate wake period is a
first intermediate wake period, the method further comprising
increasing power in the wireless communication device for a second
intermediate wake period after the second sleep period to estimate
another error of the sleep clock without performing a
demodulation.
5. The method of claim 1, further comprising during the
intermediate wake period: estimating the error of the sleep clock
based on a time that a pilot signal is received; and correcting for
the error in the sleep clock.
6. The method of claim 1, further comprising dynamically defining a
length of a slot cycle and adjusting a number of intermediate wake
periods to occur in a slot cycle based on the length of the slot
cycle.
7. A computer-readable medium comprising program code that when
executed: reduces power in a wireless communication device to place
the wireless communication device in a sleep mode for a first sleep
period; increases power in the wireless communication device to
place the wireless communication device in an intermediate wake
mode for an intermediate wake period after the first sleep period,
the intermediate wake mode being a mode in which the wireless
communication device is not fully powered and not demodulating a
paging channel but is estimating an error of a sleep clock; and
reduces power in the wireless communication device for a second
sleep period to place the wireless communication device in the
sleep mode immediately after the intermediate wake period so that
the paging channel is not demodulated by the wireless communication
device between the first sleep period and the second sleep
period.
8. The computer-readable medium of claim 7, wherein the program
code when executed increases power in the wireless communication
device for an awake period after the second sleep period.
9. The computer-readable medium of claim 8, wherein the program
code when executed during the awake period: estimates the error of
the sleep clock based on a time that a paging signal is received;
corrects for the error in the sleep clock; and causes a paging
signal to be demodulated.
10. The computer-readable medium of claim 7, wherein the
intermediate wake period is a first intermediate wake period,
wherein the program code when executed increases power in the
wireless communication device for a second intermediate wake period
after the second sleep period to estimate another error of the
sleep clock without performing a demodulation.
11. The computer-readable medium of claim 7, wherein the program
code when executed during the intermediate wake period: estimates
the error of the sleep clock based on a time that a pilot signal is
received; and corrects for the error in the sleep clock.
12. The computer-readable medium of claim 7, wherein the program
code when executed dynamically defines a length of a slot cycle and
adjusts a number of intermediate wake periods to occur in a slot
cycle based on the length of the slot cycle.
13. A controller for use in a wireless communication device having
a sleep clock, the controller comprising: means for reducing power
in the wireless communication device to place the wireless
communication device in a sleep mode for a first sleep period;
means for increasing power in the wireless communication device to
place the wireless communication device in an intermediate wake
mode for an intermediate wake period after the first sleep period,
the intermediate wake mode being a mode in which the wireless
communication device is not fully powered and not demodulating a
paging channel but is estimating an error of a sleep clock; and
means for reducing power in the wireless communication device for a
second sleep period to place the wireless communication device in
the sleep mode immediately after the intermediate wake period so
that the paging channel is not demodulated by the wireless
communication device between the first sleep period and the second
period.
14. The controller of claim 13, wherein the controller increases
power in the wireless communication device for an awake period
after the second sleep period.
15. The controller of claim 14, wherein during the awake period the
wireless communication device receives a pilot signal and a paging
signal; and the controller estimates the error in the sleep clock,
corrects for the error in the sleep clock, and causes the paging
signal to be demodulated.
16. The controller of claim 15, wherein the controller causes the
paging signal to be demodulated by assigning RAKE receiver fingers
to demodulate the paging signal.
17. The controller of claim 13, wherein the intermediate wake
period is a first intermediate wake period, wherein the controller
increases power in the wireless communication device for a second
intermediate wake period after the second sleep period to estimate
another error of the sleep clock without performing a
demodulation.
18. The controller of claim 13, wherein during the intermediate
wake period the wireless communication device receives a pilot
signal; and the controller estimates the error in the sleep clock
and corrects for the error in the sleep clock.
19. The controller of claim 13, wherein the controller dynamically
defines a length of a slot cycle, and adjusts a number of
intermediate wake periods to occur in a slot cycle based on the
length of the slot cycle.
20. An apparatus comprising: a memory that stores executable
instructions; and a processor coupled to the memory that executes
the instructions to reduce power in a wireless communication device
so as to place the wireless communication device in a sleep mode
for a first sleep period, increase power in the wireless
communication device so as to place the wireless communication
device in an intermediate wake mode for an intermediate wake period
after the first sleep period, the intermediate wake mode being a
mode in which the wireless communication device is not fully
powered and not demodulating a paging channel but is estimating an
error of a sleep clock, and reduce power in the wireless
communication device for a second sleep period to place the
wireless communication device in the sleep mode immediately after
the intermediate wake period so that the paging channel is not
demodulated by the wireless communication device between the first
sleep period and the second sleep period.
21. The apparatus of claim 20, wherein the processor executes the
instructions to dynamically define a length of a slot cycle and
adjust a number of intermediate wake periods to occur in a slot
cycle based on the length of the slot cycle.
22. The apparatus of claim 20, wherein the processor executes the
instructions to increase power in the wireless communication device
for an awake period after the second sleep period.
23. The apparatus of claim 20, wherein the intermediate wake period
is a first intermediate wake period, wherein the processor executes
the instructions to increase power in the wireless communication
device for a second intermediate wake period after the second sleep
period to estimate another error in the sleep clock without
performing a demodulation.
24. An apparatus comprising: means for reducing power in the
wireless communication device to place the wireless communication
device in a sleep mode for a first sleep period; means for
increasing power in the wireless communication device to place the
wireless communication device in an intermediate wake mode for an
intermediate wake period after the first sleep period, the
intermediate wake mode being a mode in which the wireless
communication device is not fully powered and not demodulating a
paging channel but is estimating an error of a sleep clock; and
means for reducing power in the wireless communication device for a
second sleep period to place the wireless communication device in
the sleep mode immediately after the intermediate wake period so
that the paging channel is not demodulated by the wireless
communication device between the first sleep period and the second
period.
25. The apparatus of claim 24, further comprising means for
increasing power in the wireless communication device for an awake
period after the second sleep period.
26. The apparatus of claim 25, further comprising: means for
receiving a pilot signal during the awake period; means for
estimating the error in the sleep clock during the awake period;
means for correcting for the error in the sleep clock; and means
for demodulating a paging signal during the awake period.
27. The apparatus of claim 24, wherein the intermediate wake period
is a first intermediate wake period, the apparatus further
comprising means for increasing power in the wireless communication
device for a second intermediate wake period after the second sleep
period to estimate another error in the sleep clock without
performing a demodulation.
28. The apparatus of claim 24, further comprising: means for
receiving a pilot signal during the intermediate wake period; means
for estimating the error in the sleep clock during the intermediate
wake period; and means for correcting for the error in the sleep
clock.
29. The apparatus of claim 24, further comprising means for
dynamically defining a length of a slot cycle and adjusting a
number of intermediate wake periods to occur in a slot cycle based
on the length of the slot cycle.
Description
This disclosure relates generally to wireless communication devices
and, more particularly, to sleep mode operation of a wireless
communication device.
BACKGROUND
A number of different wireless communication techniques have been
developed, including frequency division multiple access (FDMA),
time division multiple access (TDMA) and various spread spectrum
techniques. One common spread spectrum technique used in wireless
communication is code division multiple access (CDMA) signal
modulation in which multiple communications are simultaneously
transmitted over a spread spectrum radio-frequency (RF) signal.
Some example wireless communication devices that have incorporated
one or more wireless communication techniques include cellular
radiotelephones, PCMCIA cards incorporated within portable
computers, personal digital assistants (PDAs) equipped with
wireless communication capabilities, and the like.
Conserving power in a wireless communication device is a paramount
concern. To conserve power, the wireless communication device may
periodically operate in a low-power mode, often referred to as
sleep mode. When operating in sleep mode, the wireless
communication device can reduce power consumption by disconnecting
power to selected internal components. For example, slotted paging
techniques have been developed, in which paging signals are sent
from a base station to wireless communication devices within
assigned paging slots, separated by predetermined intervals of
time. Slotted paging allows a wireless communication device to
operate in sleep mode during the period of time between consecutive
paging slots without missing paging signals.
A slot cycle refers to the amount of time between successive paging
slots to be detected by a particular wireless communication device
in a slotted paging system. Slot cycles are typically on the order
of 1 to 20 seconds, but may be any length of time. For example,
slot cycles for wireless communication devices operating in data
transfer mode may be much longer than slot cycles associated with
real time radiotelephone calls because the response time of the
wireless communication device may not need to be as quick for
wireless data transfer.
During the sleep period of the slot cycle, the wireless
communication device tracks the amount of elapsed time in order to
determine the appropriate time to wake up for reception of paging
signals. Thus, even during sleep mode, the wireless communication
device consumes some power, i.e., power sufficient to track the
amount of elapsed time. The system clock of the wireless
communication device is typically a relatively high frequency, high
power clock such as a voltage controlled temperature compensated
crystal oscillator (VCTCXO). Unfortunately, a VCTCXO or other high
frequency, high quality clock may consume excessive amounts of
power.
To further reduce power consumption during sleep mode, a wireless
communication device may implement a relatively low frequency, low
power clock that operates specifically during sleep mode, allowing
the high power clock to be powered down along with other internal
components of the wireless communication device during the sleep
mode. However, low frequency, low power clock signals typically
suffer from considerable variation and/or drift, making it more
difficult to accurately track the amount of elapsed time during
sleep mode.
SUMMARY
In general, this disclosure describes various sleep mode techniques
that can be implemented in a wireless communication device. The
techniques can reduce power consumption of the wireless
communication device by facilitating the use of a relatively low
frequency, low power clock during sleep mode. For example, power
can be reduced in a wireless communication device for a first sleep
period and then increased for an intermediate period after the
first sleep period to enable estimation of an error in the sleep
clock. Sleep clock error is sometimes referred to as a slew. During
the intermediate period, demodulation of paging signals can be
avoided to conserve power. After the intermediate period, power can
be reduced in the wireless communication device for a second sleep
period. After one or more sleep periods and intermediate periods,
the wireless communication device can be powered up for full awake
mode to detect and demodulate paging signals.
The techniques may be implemented in hardware, software, firmware,
or any combination thereof. If implemented in software, the
techniques may be directed to a computer readable medium carrying
program code, that when executed, performs one or more of the
techniques described below. In that case, the techniques may be
embodied in computer readable instructions. A memory may store the
instructions, and a processor coupled to the memory may execute the
instructions to perform one or more of the techniques.
Additional details of these and other embodiments are set forth in
the accompanying drawings and the description below. Other
features, objects and advantages will become apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating a wireless communication
system.
FIG. 2 is a block diagram illustrating an exemplary wireless
communication device.
FIG. 3 is a block diagram illustrating exemplary RAKE receiver
fingers of a demodulator within a wireless communication
device.
FIG. 4 is a flow diagram illustrating a technique implementing the
concept of an intermediate wake mode within a wireless
communication device.
DETAILED DESCRIPTION
FIG. 1 is a block diagram illustrating an exemplary wireless
communication system 10. For example, system 10 may be designed to
support one or more wireless communication standards such as CDMA,
FDMA, TDMA, one or more high speed wireless data standards, or any
other wireless communication standard. As shown in FIG. 1, system
10 may include a base station 12 that transmits and receives
signals 14 to and from a wireless communication device (WCD)16 via
one or more paths. WCD 16 may implement a RAKE receiver to track
multi-path signals, e.g., the same signal propagating over
different paths and possibly received at different times. For
example, WCD may receive signal 14A from base station 12 via a
first path, as well as signal 14B via a second path caused by
reflection of signal 14C from an obstacle 18. Obstacle 18 may be
any structure proximate to subscriber unit 16 such as a building,
bridge, car, or even a person.
By way of example, CDMA standards that system 10 may be designed to
support may include one or more of the following: (1) the
"TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard
for Dual-Mode Wideband Spread Spectrum Cellular System" (the IS-95
standard), (2) the "TIA/EIA-98-C Recommended Minimum Standard for
Dual-Mode Wideband Spread Spectrum Cellular Mobile Station" (the
IS-98 standard), (3) the standard offered by a consortium named
"3rd Generation Partnership Project" (3GPP) and embodied in a set
of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G
TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (4) the standard
offered by a consortium named "3rd Generation Partnership Project
2" (3GPP2) and embodied in a set of documents including "TR-45.5
Physical Layer Standard for cdma2000 Spread Spectrum Systems," the
"C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000
Spread Spectrum Systems," and the "C.S0024 CDMA2000 High Rate
Packet Data Air Interface Specification" (the CDMA2000 standard),
(5) the HDR system documented in TIA/EIA-IS-856, "CDMA2000 High
Rate Packet Data Air Interface Specification," and (6) some other
standards.
In addition, system 10 may be designed to support standards such as
the GSM standard or related standards, e.g., the DCS1800 and
PCS1900 standards. GSM systems employ a combination of FDMA and
TDMA modulation techniques. System 10 may also support other FDMA
and TDMA standards. In some embodiments, WCD 16 may be implemented
as a hybrid access terminal (HAT) that supports multiple standards.
For example, WCD 16 may support the 1x-CDMA2000 standard for voice
communications and the IS856 standard for high-speed data
communications. The IS856-compliant system can be co-located or
overlaid in some other manner with the 1x-CDMA2000 network to
provide enhanced high-speed data services.
WCD 16 may take the form of a cellular radiotelephone, a satellite
radiotelephone, a PCMCIA card incorporated within a portable
computer, a personal digital assistant (PDA) equipped with wireless
communication capabilities, or the like. Base station 12 (sometimes
referred to as a base transceiver system, or BTS) may include a
base station controller (not shown) that provides an interface
between base station 12 and a public switched telephone network.
System 10 may include any number of WCDs and base stations.
System 10 may implement slotted paging, in which base station 12
sends paging signals to WCD 16 within assigned paging slots
separated by predetermined intervals of time. Slotted paging allows
WCD 16 to operate in sleep mode during periods of time between
consecutive paging slots without missing paging signals. In other
words, WCD 16 operates in a sleep mode and periodically wakes up at
times corresponding to the time when paging signals are expected.
Received paging signals can be demodulated in order to identify
whether information or data is to be sent to WCD 16. If so, WCD 16
may remain in awake mode to receive the information. For example,
if WCD 16 is a radiotelephone, the paging signal can inform WCD 16
of an incoming call, at which time a wireless link, or the like,
can be established to effectuate wireless communication between the
caller and a user of WCD 16.
WCD 16 may receive paging signals over a paging channel as outlined
above, and may also receive pilot signals over a pilot channel.
Pilot signals generally refers to signals comprising a repetitive
pseudo-noise (PN) sequence used for various synchronization
purposes. In some cases, the pilot signals may be use to estimate
an error in the sleep clock of WCD 16. For example, the time that a
pilot signal is received may be compared to an expected time in
order to define an error in the sleep clock. This estimation of the
error in the sleep clock may occur in various modes of operation of
WCD 16, including awake mode, and intermediate wake mode as
outlined below. In intermediate wake mode, however, various tasks
such as demodulation of the paging channel can be avoided
specifically to conserve power.
In particular, as described in greater detail below, WCD 16
periodically implements a mode of operation referred to herein as
an intermediate wake mode. Intermediate wake mode is a mode of
operation of WCD 16 that is different from a normal-awake mode
(normal-awake mode is also referred to herein as full-awake mode or
simply awake mode). During intermediate wake mode, WCD 16 wakes up
long enough and with sufficient power to estimate an error
associated with its sleep clock. For example, as mentioned WCD 16
can compare the time that a pilot signal is received with the time
it is expected to estimate the error of the sleep clock. However,
during intermediate wake mode, WCD does not necessarily perform one
or more tasks associated with a normal-awake mode, such as
demodulation of the paging signals. Instead, after estimating the
error associated with its sleep clock and correcting for the error,
WCD 16 returns to low power sleep mode, i.e., a second sleep
period.
The ability to periodically operate in an intermediate wake mode
can provide a number of advantages to WCD 16. For example,
intermediate wake mode consumes significantly less power than
normal-awake mode. The reduction in power consumption may be due to
one or more of a number of factors. For example, intermediate wake
mode may last a shorter amount of time than a normal-awake mode.
Moreover, because demodulation is not performed during intermediate
wake mode, a demodulator, e.g., including a number of RAKE receiver
fingers, may remain without power or in a low power state during
the intermediate wake mode. In this manner, power can be conserved
during intermediate wake mode.
Intermediate wake mode can also facilitate the use of lower cost
sleep clocks, particularly when relatively large slot cycles are
defined. A slot cycle refers to the amount of time between
successive paging slots to be detected by WCD 16 in a slotted
paging system. As the size of a slot cycle is increased, the
frequency error of the sleep clock becomes more problematic. In
particular, when the slot cycle is large, the frequency error of
the sleep clock may cause WCD 16 to wake up at the wrong time,
i.e., too early or too late. In either case, WCD 16 may not receive
the paging signals, and may need to remain in an awake state for
extended time (possibly for the next full slot cycle) to ensure
that the next paging signal is received. Extended awake mode can
result, however, in inefficient use of power.
The implementation of one or more intermediate wake periods over
the course of a slot cycle can ensure that WCD 16 is adequately
accounting for the frequency error of its sleep clock, thereby
ensuring that WCD 16 will be awake when the paging signal is
expected. In this manner, the implementation of intermediate wake
mode can facilitate the use of lower cost sleep clocks and the
implementation of longer slot cycles.
FIG. 2 is an exemplary block diagram of WCD 16 configured to
support one or more CDMA standards. As shown, WCD 16 includes a
radio frequency transmitter/receiver 20, a radio frequency antenna
22, a controller 24, a search module 26 and a demodulator 28. WCD
16 may also include one or more clocks such as system clock 31 and
sleep clock 32. In some cases, a single clock can operate as both
system clock 31 and sleep clock 32. However, by implementing a
lower power, low frequency sleep clock 32, power can be conserved
during sleep mode by powering off the higher frequency system clock
31. By way of example, system clock 31 may comprise a voltage
controlled temperature compensated crystal oscillator (VCTCXO)
operating at a frequency of approximately 19.68 megahertz, although
it is not limited in that respect. Also, by way of example, sleep
clock 31 may comprise a low power oscillator operating at a
frequency in the range of 30 kilohertz to 60 kilohertz, or 1.92
megahertz to 3.84 megahertz, although it is not limited in those
respects.
WCD 16 may also include one or more memory devices 34 for storing
computer readable instructions that can be executed by a processor,
for example, within controller 24. In that case, the processor may
be directly coupled to memory device 34. The functions of
demodulator 28, search module 26 and controller 24 may be
implemented by one or more digital signal processors (DSP),
discrete hardware circuitry, firmware, field programmable gate
arrays (FPGA), software executing on a programmable processor such
as a DSP, or a combination of any of the above.
During operation in awake mode, antenna 22 receives incoming
signals, such as paging signals and pilot signals transmitted from
base station 12. Transmitter/receiver 20 includes circuitry to
process received signals and output digital values.
Transmitter/receiver 20 may process the received signal using a
low-noise amplifier (LNA), an RF mixer and an analog-to-digital
(A/D) converter (not shown in FIG. 2) to produce corresponding
digital values. The digital values may comprise a train of pulses
sometimes referred to as "chips."
WCD 16 can use search module 26 to continuously scan an incoming
spread spectrum signal in the time domain to determine the
existence, time offset, and signal strength of various received
paths. Search module 26 records and reports the path information to
controller 24 as search results. Local maximum energy peaks,
representing received paths, appear for time offsets that result in
recovery of a received signal, while other time offsets typically
result in little or no signal energy. In a multi-path environment,
signal reflections or echoes may cause multiple energy peaks to
occur.
WCD 16 can implement RAKE receiver fingers to track signals of a
multi-path environment. For example, as illustrated in FIG. 3,
demodulator 28 may include a number of demodulation elements 30
(referred to as fingers) to track multi-path signals. In that case,
controller 24 uses the search results generated by search module 26
to assign demodulation elements 30 within demodulator 28. The
demodulation elements 30 track and demodulate signals associated
with one or more of the signal paths.
Referring again to FIG. 2, controller 24 can forward received chips
to demodulator 28 for a process referred to as demodulation.
Demodulation may involve despreading of pseudo-noise (PN) codes and
decovering of orthogonal codes for each chip (sometimes referred to
as "Walsh decovering"). The results of demodulation are then
colleted and grouped into symbols. For example, each symbol may be
generated from a stream of 256 demodulated chips. If WCD 16
implements a RAKE receiver configuration like that illustrated in
FIG. 3, demodulation occurs in each demodulation element 30. In
that case, the demodulated results from each path of the multi-path
can be combined by combiner 38.
WCD 16 can be configured to operate according to slotted paging
techniques. As mentioned above, in slotted paging, WCD 16 powers up
to receive and demodulate paging signals. However, the paging
signals are not transmitted to WCD 16 at all times. Rather, the
paging signals are transmitted during temporally defined slots.
Thus, during the time between the slots, WCD 16 can enter a sleep
mode without missing the paging signals. During sleep mode,
controller 24 may reduce or eliminate power consumption of various
internal components of WCD 16, including for example,
transmitter/receiver 20, search module 26, demodulator 28 and
system clock 32.
At a time just before a paging signal is expected, controller 24
can cause the various internal components to power up so that the
paging signal and other signals such as pilot signals can be
received. For example, upon powering up, WCD may use pilot signals
received over a pilot channel to estimate an error in sleep clock
32 in order to provide an open loop feedback adjustment as
described in greater detail below. Then, after adjusting for the
sleep clock error, the paging signal can be demodulated in order to
determine whether WCD 16 is being paged for wireless communication.
If so, WCD 16 can remain in an active state so that signals
containing information, e.g., voice or data signals, can be
transmitted to WCD 16. However, if the paging signal does not
indicate that information is to be sent to WCD 16, controller 24
can cause WCD 16 to return to a sleep mode for a period of
time.
During the sleep period, system clock 31 may be powered down along
with a number of other internal components of WCD 16. In that case,
sleep clock 32 can be used to track the amount of time that has
elapsed. The process can continue for any number of slot cycles,
with WCD 16 periodically entering awake mode to receive the paging
signals and then returning to sleep mode if the paging signal does
not indicate that information is to be sent to WCD 16.
The error associated with sleep clock 32 may be caused by frequency
drift, or other frequency errors may occur in sleep clock 32 as a
result of such things as temperature variations. Moreover, because
the internal components of WCD 16 can generate heat, the frequency
errors associated with sleep clock 32 may become relatively
significant even over relatively short time periods. The error
associated with sleep clock 32 is typically quantified in parts per
million (PPM). As slot cycles become larger, the effective error
per slot cycle of the sleep clock becomes larger even if the error
in PPM remains the same.
Each time WCD 16 enters awake mode, the error associated with sleep
clock 32 can be calculated to provide an open loop feedback
adjustment. For example, the error associated with sleep clock can
be measured for a slot cycle by comparing the expected time that a
signal should be received (as defined by sleep clock 32) with the
actual time it is received. In particular, WCD 16 may detect one or
more unique words within the pilot signal or paging signal, such as
a message preamble which signifies the beginning of the signal. The
time that the unique word was received can then be compared with an
expected time to measure the error of sleep clock 32. The measured
error can then be used to adjust the amount sleep time (as defined
by sleep clock 32) for the next sleep period, such as by adding an
offset value to the sleep period.
WCD 16 typically remains in an awake mode for a window of time
around the time that the paging signal is expected in order to
ensure that paging signals can be received even if the frequency
drift of sleep clock 32 causes the WCD 16 to awake slightly too
early or slightly too late. However, if the PPM of sleep clock 32
is too large or if the length of the slot cycle is too large,
problems can arise. Specifically, the error associated with sleep
clock 32 can cause WCD 16 to awake at the wrong time, such that the
paging signal is missed altogether. In that case, WCD 16 may need
to remain in awake mode for a period of time covering the next full
slot cycle in order to ensure that the next paging signal is not
also missed, which results in additional power consumption.
One possible solution to this problem is to implement a higher
frequency sleep clock within WCD 16, particularly if the slot cycle
is defined to be relatively large. However, higher frequency sleep
clocks may be more costly and typically use more power than lower
frequency sleep clocks.
Another possible solution is to increase the size of the window of
time that WCD 16 remains in awake mode by an amount sufficient to
ensure that the paging signal will not be missed. However, as WCD
16 remains in awake mode for longer periods of time, more power is
consumed. Moreover, the length of the slot cycle may change over
time making it difficult to optimize the size of the window.
In accordance with one embodiment, WCD 16 is capable of
periodically operating in intermediate wake mode for one or more
intermediate periods of time within slot cycles. The ability to
operate in intermediate wake mode may allow WCD 16 to utilize a
lower power, lower frequency sleep clock, even if large slot cycles
are defined. WCD 16 periodically operates in intermediate wake mode
in order to estimate and account for errors in sleep clock 32.
However, additional tasks, such as demodulation are avoided during
the periods of time associated with intermediate wake mode.
FIG. 4 is a flow diagram according to one embodiment. In
particular, FIG. 4 illustrates a process that can be implemented
within controller 24 to control the mode of operation of WCD 16
over the course of a slot cycle. Over the course of the slot cycle,
WCD 16 may operate in one or more of the following modes: sleep
mode, awake mode, and intermediate wake mode. As shown, at the
beginning of the slot cycle, controller 24 reduces power for a
sleep period within WCD 16 (41). For example, controller 24 may
cause various internal components to power down or otherwise enter
a low power state. Sleep clock 32 remains powered during sleep
mode, however, and provides a measure of the amount of time that
has elapsed. Controller 24 may provide an adjustment to sleep clock
32 based on an error estimated for the previous slot cycle. After a
defined length of time, controller 24 may cause some or all of the
internal components of WCD 16 to be powered up. The specific
components that are powered up and the length of time that they
remain powered depends on whether WCD 16 enters an awake mode or an
intermediate wake mode (illustrated by decision box 42).
If WCD 16 enters intermediate wake mode (42), controller 24 causes
WCD to increase power for an intermediate awake period (43). In
intermediate wake mode some, but not all of the internal components
are powered up. For example, demodulator 28 may remain in a low
power state for the intermediate period. WCD 16 can receive an
incoming pilot signal (44), and reception of the pilot signal can
be used to estimate the sleep clock error (45). For example,
controller 24 can compare the expected time that the pilot signal
should be received (as defined by sleep clock 32) with the actual
time it is received. In particular, WCD 16 may define a window of
time during which the pilot signal should be received. The time
that the pilot signal is expected may be defined by a pseudo-noise
(PN) offset value associated with the base station sending the
signal. WCD 16 may store the PN offset value prior to entering
sleep mode. Then, when WCD 16 enters intermediate wake mode, it can
use the stored PN offset to define the expected time for the pilot
signal. The time that the pilot signal is actually received can be
compared with an expected time to measure the error of sleep clock
32.
Controller 24 can then correct for the error in sleep clock 32 for
the next sleep period (46), such as by implementing a feedback
loop. In other words, the measured error can be used to adjust the
timing for the subsequent sleep period, such as by adding an offset
to the sleep period defined by sleep clock 32. After controller 24
has corrected for the error in the sleep clock, it can cause WCD to
reenter sleep mode, i.e., reduce power of a second sleep period for
that slot cycle (41). In other words, during intermediate wake
mode, WCD 16 does not perform demodulation. For at least this
reason, intermediate wake mode may consume significantly less power
than full-awake mode.
WCD 16 may implement any number of intermediate wake periods over
the course of a slot cycle. In this manner, errors associated with
sleep clock 32 can be accounted for, even if the slot cycle is very
large. Eventually, WCD 16 enters full-awake mode (42). In that
case, controller 24 causes WCD 16 to increase power for an awake
period (47). In awake mode, substantially all of the internal
components are powered up, including demodulator 28.
During awake mode, WCD 16 may perform all of the tasks performed
during intermediate wake mode, such as receiving a pilot signal
(48), estimating the sleep clock error (49), and correcting for the
error in the sleep clock (50), for example, by implementing a
feedback loop to compensate timing of the next sleep period. In
addition, during awake mode, WCD 16 performs additional tasks not
performed during intermediate wake mode. In particular, during
awake mode, WCD 16 performs demodulation of the paging signal. For
example, control unit 24 may assign RAKE receiver fingers (51)
which can demodulate the paging signal (52), such as by despreading
of pseudo-noise (PN) codes and Walsh decovering of orthogonal
codes. The demodulated symbols can then be interpreted in order to
determine the content of the paging signal.
If the content of the paging signal indicates that information is
to be sent to WCD 16, WCD 16 can remain in awake mode to receive
the information. However, if the content of the paging signal
indicates that no information is to be sent to WCD 16, controller
24 can cause WCD 16 to enter a sleep period for the next slot
cycle.
Again, by operating in intermediate awake mode during one or more
intermediate wake periods over a course of a slot cycle, sufficient
accounting of the error associated with sleep clock 32 can be
achieved, even if a very low power, low frequency sleep clock is
implemented, and even if large slot cycles are defined. The number
of intermediate wake periods implemented over the course of a slot
cycle may depend on both the accuracy of the sleep clock and the
length of the slot cycle. In most cases, intermediate wake mode
should be invoked often enough to account for the sleep clock error
and thereby ensure that the paging signal can be received during
the window of time allocated for the reception of the paging
signal.
In some cases, WCD 16 may dynamically control the number of
intermediate wake periods based on the length of the slot cycle.
For example, WCD 16 may implement what is referred to as a
telescoping algorithm to adjust the length of the slot cycle over
the course of operation in the slotted paging system. In one
example, the length of the slot cycle is defined by a slot cycle
index (SCI). For example the length of the slot cycle may be
approximately:
1.28*2.sup.(SCI) seconds
Thus, if SCI=0, then the length of the slot cycle is approximately
1.28 seconds, and if SCI is 1, then the length of the slot cycle is
approximately 2.56 seconds. If SCI is 2, then the length of the
slot cycle is approximately 5.12 seconds, and so forth.
WCD 16 may implement a telescoping algorithm to dynamically control
the length of the slot cycle. The telescoping algorithm may operate
within control unit 24 to adjust the SCI over the course of time in
order to improve performance of WCD 16. For example, in one
embodiment, the telescoping algorithm begins with SCI=0 and then
increments the SCI for subsequent slot cycles when appropriate. The
effect of the algorithm generally causes the length of the slot
cycle to increase over time, when appropriate. In particular, the
telescoping algorithm may cause the slot cycle index to be
incremented only after the error in the sleep clock has settled to
a relatively steady state. The telescoping algorithm may cause WCD
16 to sleep for longer and longer periods of time, after
determining that appropriate account of errors in the sleep clock
are made. At some point, the telescoping algorithm should reach a
desired slot cycle, at which point increments to the slot cycle
index may cease. The desired slot cycle index may be programmed
into WCD 16 and base station 12. In other words, the telescoping
algorithm can provide an acceptable way to reach the desired slot
cycle index in a step-wise fashion, while accounting for possible
errors in the sleep clock.
In accordance with one embodiment, control unit 24 may also
dynamically adjust the number of intermediate wake periods based on
the adjusted length of the slot cycle, as dynamically defined by
the telescoping algorithm. For example, if a low accuracy sleep
clock is used, it may be desirable to adjust for errors in the
sleep clock approximately every 1.28 seconds, regardless of the
defined length of the slot cycle. In that case, if the telescoping
algorithm establishes a SCI=0, then no intermediate wake periods
are necessary over that slot cycle. However, if SCI is adjusted to
SCI=1, control unit 24 may invoke an intermediate wake mode for one
intermediate period of that slot cycle. Similarly, if SCI is
adjusted to SCI=2, control unit 24 may invoke intermediate wake
mode for three different periods of that slot cycle. In this
manner, it can be ensured that the errors in the sleep clock are
adjusted approximately every 1.28 seconds, regardless of the
defined length of the slot cycle. This can ensure that the errors
associated with the sleep clock are adequately accounted for,
regardless of the length of the slot cycle.
Various embodiments have been described. For example, an
intermediate wake mode of operation of a wireless communication
device has been described. As outlined above, implementing
intermediate wake mode can improve performance of a wireless
communication device, particularly when used in a slotted paging
system. Nevertheless, modifications can be made without departing
from the sprit and scope of this disclosure. For example,
additional frequency error estimation techniques may be implemented
to improve estimation of the frequency error of the sleep clock. In
one example, early re-activation of system clock 31 following a
sleep mode may provide a measurement of the actual frequency of
sleep clock 32 to improve error estimation. These and other
embodiments are within the scope of the following claims.
* * * * *